Surprise is nice, but in my case I have to take an hour long train to and from conventions that I go to, so I usually wear my costumes to the convention. The one plush side to wearing your costume out of the competition is that you can get pictures, and sometimes photographers will request a photo shoot. To be honest, its really all about preference. In my case, for Fan Expo this year I want to wear my Raven (DC Comics) costume all throughout Saturday (day of competition) because I know there are lots of fans of the character. Anyways, hope this helps.